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Mitosis

Mitosis is the portion of the cell cycle responsible for cell division and the production of two new daughter cells. Mitosis consists of several phases (view Figure 1):

  1. Prophase: During this phase, the nuclear membrane and nucleolus begin to disintegrate and the centrioles in the cell move to each end as the chromatin condenses. The mitotic spindle (made of microtubules) begins to form and attaches to the now condensed chromosomes. The kinetochores of the chromosomes, a protein structure assembled on the centromere of a chromosome (links two sister chromatids together), are where the spindle fibers attach.
  2. Metaphase: Once prophase is completed, the spindle microtubules position the chromosomes so that they are in the center of the cell.
  3. Anaphase: In anaphase, the chromatids of each chromosome get pulled apart, with one pair moving to each end of the cell. This happens because the microtubules, which are positioned on the kinetochore of each chromosome, pull in the chromatids as they shorten in length. The cell also becomes stretched in this phase by the unattached microtubules.
  4. Telophase: During this phase, a couple of things happen. First off, the chromatids (chromosomes) reach each of the poles. Secondly, the cell is continually being stretched by the unattached microtubules. Thirdly, the chromosomes begin to de-condense as the DNA unwinds and as the nucleoli reappear, nuclear membranes begin to reform.
  5. Cytokinesis: This process differs in animal and plant cells, but essentially it is this phases of mitosis which splits the cytoplasm so that two new daughter cells form. In animal cells, the cell becomes pinched into two as a furrow forms in the middle of the cell. A furrow is unable to form in plant cells because of their cell walls. Therefore, during telophase, a cell plate is fused in the center of the cell and this cell plate continues to grow until it fuses with the plasma membrane. Once completed the cell divides into two.

Figure 1. This diagram presents all of the phases of mitosis and also includes interphase and the G0 phase in terms of where they fit within the total process of the cell cycle. This image has been taken from http://commons.wikimedia.org/wiki/File:Mitosis_diagram.jpg